1. Field of the Invention
This invention relates to improvements in or relating to solar energy converters, and in particular concerns an absorber for solar energy converters having an internal chamber through which a heat exchange fluid may be passed.
It has been known for many years that the sun provides an enormous amount of energy in the form of visible and invisible radiation to the earth's surface, and that this energy may be converted into other forms of energy such as heat and electricity. In recent years the increased cost of conventional fuels has resulted in great interest in the utilization of the sun's energy for commercial and domestic purposes.
2. Description of the Prior Art
Photoelectric devices are well known for use in converting light energy directly into electrical energy, but such devices are expensive. Moreover, for many applications it is more convenient to convert the sun's energy into heat energy.
A simple known form of apparatus for effecting the conversion to heat energy comprises a flat plate arranged to absorb solar radiation so that the plate is heated. By contacting the plate with a heat exchanger this heat may be put to use. However, this type of arrangement is highly inefficient in transferring energy to the heat exchanger as the plate also tends to re-radiate energy as its temperature rises.
A more sophisticated device for utilizing the sun's energy comprises a reflector which collects and focuses solar radiation onto an element which absorbs the radiation and is thus heated. By contacting the heated element directly or indirectly with a heat exchange fluid the heat may be extracted and then utilized in a variety of ways. Devices of this type are known as "solar energy converters" and the element which absorbs the focussed radiation is referred to herein as the "absorber".
The reflector of a solar energy converter is usually a concave mirror with either a circular or parabolic curvature, and the absorber is arranged at the focus of the mirror. A conventional arrangement employs a mirror concavely curved in one direction only, and thus generally part-cylindrical in shape, which focuses the sun's rays to a focal line parallel to the mirror surface. The absorber is then located along this focal line. Typically the absorbers are in the form of tubes through which a heat transfer fluid is passed.
Various forms of tubular absorbers are known. The simplest known form comprises a cylindrical tube through which the heat exchange fluid may be passed. However, although such a cylindrical tube presents a convex surface to the mirror which is effective at absorbing radiation, it also has a convex surface directed away from the mirror and this acts as a radiator giving rise to considerable heat losses from the absorber. More complex tubular members having star-shaped cross-sections have also been employed with a view to increasing the radiation-receiving surface, but such arrangements merely compound the shortcomings of the cylindrical absorber by increasing the radiating surface of the absorber.
Thus, known forms of solar energy converter tend to be inefficient, extracting only a small proportion of the available energy from the sun's radiation, principally because of the inefficiency of the absorbers used and at least in part this results from radiated heat loss from the absorber.